Trying to understand efibootmgr

hazel · 05-31-2019, 12:00 PM

When I type "efibootmgr -v" in Slackware, I get:

Code:

BootCurrent: 0005
Timeout: 2 seconds
BootOrder: 0000,0005,0003,0002,0001
Boot0000* Windows Boot Manager  HD(2,1f4800,82000,88e50bfb-f30c-4915-9628-1712260476df)File(\EFI\Microsoft\Boot\bootmgfw.efi)WINDOWS.........x...B.C.D.O.B.J.E.C.T.=.{.9.d.e.a.8.6.2.c.-.5.c.d.d.-.4.e.7.0.-.a.c.c.1.-.f.3.2.b.3.4.4.d.4.7.9.5.}...l................
Boot0001* Windows Boot Manager  Vendor(99e275e7-75a0-4b37-a2e6-c5385e6c00cb,)
Boot0002* UEFI: IPV6 Realtek PCIe GBE Family Controller ACPI(a0341d0,0)PCI(1c,2)PCI(0,0)MAC(c03fd5e6c930,0)030d3c000000000000000000000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000..BO
Boot0003* UEFI: IPV4 Realtek PCIe GBE Family Controller ACPI(a0341d0,0)PCI(1c,2)PCI(0,0)MAC(c03fd5e6c930,0)IPv4(0.0.0.0:0<->0.0.0.0:0,0, 0..BO
Boot0005* Slackware     HD(2,1f4800,82000,88e50bfb-f30c-4915-9628-1712260476df)File(\EFI\Slackware\elilo.efi)

The two Windows entries are obsolete and I will delete them eventually, but I don't want to modify anything until I understand the setup better. Note that there is no CD option here.

If I boot from a CD and run the same command, I get:

Code:

BootCurrent: 0006
Timeout: 2 seconds
BootOrder: 0006,0000,0005,0003,0002,0001
Boot0000* Windows Boot Manager  HD(2,GPT,88e50bfb-f30c-4915-9628-1712260476df,0x1f4800,0x82000)/File(\EFI\Microsoft\Boot\bootmgfw.efi)WINDOWS.........x...B.C.D.O.B.J.E.C.T.=.{.9.d.e.a.8.6.2.c.-.5.c.d.d.-.4.e.7.0.-.a.c.c.1.-.f.3.2.b.3.4.4.d.4.7.9.5.}...l................
Boot0001* Windows Boot Manager  VenHw(99e275e7-75a0-4b37-a2e6-c5385e6c00cb)
Boot0002* UEFI: IPV6 Realtek PCIe GBE Family Controller PciRoot(0x0)/Pci(0x1c,0x2)/Pci(0x0,0x0)/MAC(c03fd5e6c930,0)/IPv6([::]:<->[::]:,0,0)..BO
Boot0003* UEFI: IPV4 Realtek PCIe GBE Family Controller PciRoot(0x0)/Pci(0x1c,0x2)/Pci(0x0,0x0)/MAC(c03fd5e6c930,0)/IPv4(0.0.0.0:0<->0.0.0.0:0,0,0)..BO
Boot0005* Slackware     HD(2,GPT,88e50bfb-f30c-4915-9628-1712260476df,0x1f4800,0x82000)/File(\EFI\Slackware\elilo.efi)
Boot0006* UEFI: MATSHITA DVD-RAM SW830  PciRoot(0x0)/Pci(0x13,0x0)/Sata(1,65535,0)/CDROM(1,0x4d,0xb40)/HD(1,MBR,0x0,0x0,0xb40)..BO

Suddenly there is an entry for my CDROM (Boot0006). But where did it come from and why does it also seem to be regarded as a hard drive?

mrmazda · 05-31-2019, 10:05 PM

UEFI BIOS may seem mixed up more easily or often than we like, but they aren't stupid. When there is bootable removable media during POST, they would normally include it among boot selections, unless some option in BIOS setup directs it be ignored or disabled.

hazel · 06-01-2019, 07:21 AM

What surprised me was that there isn't a permanent entry for the cdrom drive. After all, the UEFI chip must be able to detect that there is a second SATA drive in the machine. Having an entry for the empty drive surely wouldn't do any more harm than those empty Windows entries. As far as I can see, UEFIs treat non-functioning boot entries the same way that BIOS's do: just try the next one on the list!

mrmazda · 06-01-2019, 06:56 PM

BIOS differ. My newest are two Kaby Lakes. The Asus' BIOS doesn't remember as much as my Gigabyte's does, which includes hard disks (2), NVME (1) devices, and labels of unattached OM and USB sticks. How many it's capable of I can't say. There are 7 total ATM (4 removables).

jefro · 06-03-2019, 05:16 PM

UEFI boot seems to grow.

sudo efibootmgr to view is fine usually.

To remove entries

sdo efibootmgr -Bb 009 for example.

Everyone has to monitor their systems if they have one that never seems to stop adding entries. I have one that will get up to 400 or so before I have to do a mass delete.